The Feasibility of Adaptive CT Simulation-Free Radiation Therapy

Abstract

To investigate the feasibility of a novel, streamlined radiotherapy treatment workflow in which simulation and treatment occur in a single on-table session. The efficiency, dosimetric accuracy, plan quality, and resource requirements were metrics used to evaluate the clinical potential of CT simulation-free radiotherapy. An adaptive radiotherapy treatment platform was upgraded to include a novel CBCT system reporting image quality and Hounsfield unit accuracy specifications comparable to standard fan-beam CT. An in-house workflow was designed to allow the CBCT data to be used as reference image sets for planning. Two test cases were completed on anthropomorphic phantoms equipped with small volume ion chambers (cross-calibrated to an ADCL traceable dose standard) to evaluate the feasibility and accuracy of the workflows. A spine was planned for palliative treatment with 8 Gy in 1 fraction, and an intact prostate was planned for definitive treatment with 60 Gy in 20 fractions. The CBCTs were acquired using default thorax and pelvis imaging protocols and reconstructed using an iterative algorithm with scatter removal. CBCTs were used for contouring and planning, and treatment was delivered via an online adaptive workflow. An extended-field CBCT acquisition can be acquired in 12 s of acquisition time and reconstructed in approximately 1 min. The superior-inferior extent for the CBCT planning images was 42 cm, which captured the full extent of relevant anatomy; an audit of recent single-site palliative CT simulation scans had an average length of 44.9 cm. The contouring and treatment planning for the spine and prostate were completed in 30 min and 23 min, respectively. The dosimetric agreement with the treatment plan agreed to within a range of -1.17 to 1.64%, and a mean and standard deviation of 0.41 ± 1.16%. Using an in-house workflow, CT simulation-free radiation therapy was shown to be feasible with acceptable workflow efficiency and dosimetric accuracy. This approach may be particularly applicable for urgent palliative treatments. With the availability of software to enable this workflow, and the continued advancement of on-treatment adaptation, single-visit radiation therapy may replace current practice for some clinical indications.